An American tank full of US Marines crashes through the silence of the sub-zero pine forest, far above the Arctic Circle, as unidentified drones hover overhead and yellow and green smoke fills the freezing air.

The troops’ target? A bunker up ahead, manned by Norwegian soldiers. Shots ring out as the Marines advance, crunching through the snow beneath gray winter skies.

It’s all role-play, of course — the maneuvers are part of a training exercise, but one jarringly imbued with the new reality along NATO’s northernmost border with Russia.

Some 300 US Marines are due to be based in Norway on a rotational basis from January, for a year, as part of a package of measures intended to reassure one of NATO’s most easterly members.

Although they’ll be about 1,000 kilometers (621 miles) from the border, the plan is for them to bolster the readiness of new “pre-positioned” tanks and weaponry stored throughout the year in underground caves.

Collective defense

But before that deployment, the US and Norway are conducting exercises above the Arctic Circle, taking Abrams tanks further north than they’ve ever been before, as part of more than a week of joint exercises.

And they are being watched intensely: Norwegian police are investigating more than 10 sightings of unidentified drones spotted observing the US and Norwegian maneuver.

A Norwegian army spokesman, Ole Johan Skogmo, said they were investigating whether the drones were related “to interested locals or other nations.”

And the reason for all this activity? In a word: Ukraine.

“In 2014, that was a clear sign that Russia has stepped in to an area where they are willing and able to use military power,” says Eldar Bernil. “Suddenly we have changed focus in particular from what was going on in Afghanistan to collective national defense.”

A senior Norwegian security official told CNN there are increasing concerns about the threat posed by Russia, after their actions in Crimea and eastern Ukraine, where small scale separatist rebellions were backed up with the discreet and deniable use of Russian military might.

“We are talking about hybrid warfare,” said the unnamed official, “which is warfare under the threshold of war, where you challenge the nature of democracy, where you have free access to social media.

“It’s a war without Article 5,” he said, referring to collective defense, the central tenet of NATO, which states that an attack on one member is an attack on all NATO allies.

“Suddenly when the tension rises, you bring in the soldiers, like you did in Crimea, and say, ‘From now on, I am responsible and I will take care of you as long as you do what I say.'”